Back in the early days of the Web, you used to have to 'submit' your website to the search engines. I remember that, back in 2001, you could pay Yahoo US $300 to fast track this process. This submission process was partially due to the directory model that early search engines such as Yahoo used. Site owners helped populate the search databases by identifying where their site fit in the directory taxonomy.
It sounds a little goofy in retrospect, doesn't it?

A client recently asked me about the relevance of venerable directories like Yahoo and DMOZ. I told them not to worry about these directories, but wanted to back myself up with a little data.

I went and checked out the web stats for a website that's been around in both directories for at least four years. The site had about 95,000 referrals in the first 8 months of 2006. 27 came from Yahoo's directory and 6 came from DMOZ.

Technically speaking, if it doesn't take you very long to submit to Yahoo, then I suppose your 15 minutes of time may be worth 27 visitors. I know other sites use DMOZ, but I don't know of any popular ones.